This invention relates generally to electrochemical machining (ECM), and more specifically, to methods and systems for forming cooling holes in a turbine engine airfoil.
Electrochemical machining and/or shaped tube electrochemical machining (STEM) is commonly used to form cooling holes in turbine engine airfoils. During an ECM process, the workpiece being machined is coupled to a positive terminal of a DC power supply and the electrode is coupled to a negative terminal of the DC power supply. An electrolyte flows between the electrode and the workpiece. For example, the electrolyte may be an acid or an aqueous salt solution. During the machining process, the workpiece is dissolved by controlled electrochemical reactions to form the cooling hole. Generally, such machining processes form cooling holes that have a substantially circular cross-sectional area. The cross-sectional area of each cooling hole is sized to provide a desired amount of flow metering through an inlet of the cooling hole. However, because such openings are generally substantially uniform throughout the blade, an amount of potential heat transfer inside the blade and/or the cooling hole may be limited by the circular cross-sectional profile of the opening.
In addition, a cooling hole having a circular cross-sectional area defined at its outlet may not be suitable for use in an airfoil having a narrow trailing edge. For example, a circular cross-sectional area defined at an outlet of a cooling hole extending through such an airfoil may induce high stress concentrations to the trailing edge of the airfoil. Accordingly, cooling holes having substantially constant circular cross-sectional areas may increase costs associated with maintaining a turbine engine and/or decrease the turbine engine life-span.